1. Field of the Invention
This invention pertains to the field of water treatment and to the use of ion (anion) exchange resins to remove contaminants such as perchlorate ions from aqueous feed stocks ranging from domestic, industrial and agricultural water supplies such as drinking water to brines and other aqueous streams. More particularly, this invention relates to the removal of perchlorate load from perchlorate-loaded resins loaded by use in water treatment so as to permit reuse or safe disposal of the resin.
2. Background Information
Ammonium perchlorate has been used for the past 50 years as an oxidizer component in solid explosives and solid propellants for rockets, missiles and fireworks. It is estimated that well over 90% of the ammonium perchlorate produced in the United States is used in these applications. Casual handling of perchlorates and perchlorate-laden effluents by manufacturers, and the build up of poorly-contained stockpiles of outdated missile and rocket fuels have resulted in perchlorate contamination of surface water and ground water supplies. Perchlorate contamination is a growing problem in at least 14 Western states in the United States and has been reported in Europe as well.
The California Department of Health Services has established an action level for perchlorate of 18 ug/l. This is based upon the potential for perchlorate to inhibit the uptake of iodine by the thyroid gland. Perchlorate levels of up to several hundred ug/l have been found in ground water in California and other states.
Two approaches to removing perchlorate from water supplies are being researched extensively—biological destruction and ion exchange. Biological destruction using various bacterial strains has been described at the Federal Remediation Technologies Roundtable General Meeting held on May 30, 2001 where Jeffrey Marqusee described how biological organisms could attack perchlorate in subsurface environments. Similar studies were also reported at that meting by Paul Hatzinger (Poster Number 43) and by John D. Coates (Poster Cleanup CU 45).
Ion exchange is attractive because perchlorate has a very high affinity for common polystyrene-based strong base anion exchange resins. However, state of the art practice does not provide a practical and convenient method for regeneration of the resin. This is due at least in part to perchlorate's affinity for the common resins being so strong that very large quantities of concentrated sodium chloride brine are required to displace the perchlorate during regeneration. Several hundred pounds of sodium chloride regenerant per cubic foot of resin at salt concentrations of from 6% to saturation are typically used. Alternatively, the resins can be used once for perchlorate adsorption and then thrown away instead of being regenerated. In both cases, a difficult-to-deal-with perchlorate-loaded end product is formed. The loaded resin can not be safely discarded in ordinary land fills and the like because of fears of its perchlorate content reentering the environment. Attempts to bacterially break down the perchlorate content of the concentrated sodium chloride brine have been unsuccessful because the bacteria are generally inactivated by the high salt levels. For example, Tina M. Gingras and Jacimaria R. Batista reported in J. Environ. Monit. (2002), 4, 96-101, that as little as 0.5% sodium chloride present in a bioremediation environment lowered perchlorate degradation activity by 30% while 1.0% sodium chloride reduced activity by 60%.
What is needed, and what this invention provides, is a process for removing perchlorate from perchlorate-loaded ion exchange resins without generating large quantities of intractable regeneration products. This invention also provides a new form of ion exchange resin which is capable of removing perchlorate ions from solution and directly breaking the perchlorate down to nonperchlorate species in situ.